Monarch Butterflies

Monarch butterflies (Danaus plexippus) of North America are renowned for their long-distance seasonal migration and spectacular winter gatherings in Mexico and California. The monarch butterfly population has recently declined to dangerously low levels. In the 1990s, estimates of up to one billion monarchs made the epic flight each fall from the northern plains of the U.S. and Canada to sites in the oyamel fir forests north of Mexico City, and more than one million monarchs overwintered in forested groves on the California Coast. Now, researchers and citizen scientists estimate that only about 56.5 million monarchs remain, representing a decline of more than 80% from the 21 year average across North America.

Area occupied by monarchs in Mexico from 1994-2015 (left) and population censuses of western monarchs from 1997-2014 (right). Click to enlarge.

To conserve this animal and its habitat, Xerces works with multiple partners across North America. We believe that by working broadly with multiple stakeholders, we are well-positioned to truly recover these butterflies. See The Xerces Society’s Partnerships for Monarchs for a summary of our recent efforts and ongoing partnerships.

Nationally, Xerces is working to restore monarch breeding habitat. Our partnership with the USDA NRCS, has resulted in planting more than 120,000 acres of habitat for monarchs and other pollinators, including tens of thousands of diverse wildflower plantings that include milkweed. We are also working to increase the availability of native seed and to make it less expensive to use in restoration activities.

The primary threats to the monarch butterfly include the loss of milkweed—the key plant that monarch caterpillars need to survive—from agricultural and natural areas, degradation of overwintering sites, and climate change. The large-scale use of systemic insecticides such as neonicotinoids within the breeding range of the monarch may pose a considerable threat. Natural enemies such as diseases, predators, and parasites likely also influence the size of the monarch population. Loss of milkweed from the American Midwest is primarily due to the dramatic increase in the use of the herbicide Roundup™ (glyphosate), made possible by the mass-planting of Genetically Modified Herbicide Tolerant corn and soy. Illegal logging has threatened overwintering sites in Mexico, and in California, numerous sites have been logged and replaced with housing developments. Extreme weather events may be negatively impacting monarchs in the eastern U.S. and low monarch populations in California are correlated with years of intense drought. Climate change models predict that future climate scenarios will not be suitable to support overwintering monarchs or the oyamel fir trees that they use in Mexico.